Loading coil



H. BUSCH ET AL ZDC. s, 1931.

LOADING COIL Filed May 14, 1950 BY @m y ATTORNEY Patented Dec. 8, 3193i res ease HAN S B'USCH, OF DARMSTADT, AND ALFRED IBYK, 0F BERLIN-CEARLOTTENBURG, GER- MANY, ASSIGNORS TO GENERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORK LOADING- COIL Application filed May 14, 1930, Serial No. 452,492, and in Germany May 27, 1929.

The usual loading coils for transmission lines contain two windings, one of which is connected in the outgoing conductor and the other in the return conductor of a circuit. In

E such a case, extremely high demands are put on the symmetry of the coils, that is, on the exact similarity of the electrical properties of the two windings.

From other apparatus, for instance, teleb phone transformers, a simple means is known for obtaining such symmetry to a very high degree. For this purpose, the two windings are made by winding two wires bifilarly together This means has, however, hitherto ij not been employed for loading coils and the reason for not doing this is because the very close position of the two wires on the whole of their length causes a high capacity of the two windin s in respect to each other. In the case J of loadlng coils, such capacity has been rearded as a drawback, because, as is well own, the purpose of the insertion of loading coils is to compensate for the detrimental influence of capacity on the transmission of 5 the speaking-currents. Consequently a high self-capacity of the coils, would be looked upon as a step in the wrong direction.

The subject of the inventionis a loading coil the two halves of the windings of which 0 consist of two wires which are wound .bi-

filarly together, in spite of the above-mentioned considerations. The invention is based on the conception that a line which is provided with such coils possesses a considerable ad- 5 vantage, namely, that the transmission delay for the various frequencies involved is brought more nearly to the same value, whereas the above-described disadvantages can be obviated by correspondingly greater dimensioning of the coils or reduction of the distance between the coils.

It is well known that tendencies to resonant efiects in telephone lines lead to phase distortion, which, in the case of long lines,

5 causes considerable distortion of speech, and,

therefore, in the case of long-distance cablelines, one is forced either to apply particularly weak loading or to avoid phase distortion by special artificial circuits (p'hase-eompen sation) It is further well known that this can be obtained, for example, by connecting condensers to the loading coils in a'certain manner. According to the present invention the self-capacity of a bifilarly wound loading coil can, with suitable arrangement, be laid or dimensioned in such a Way as 'is required for this purpose, so that the insertion of special condensers is, in general, superfluous.

In the accompanying drawings, Fig. 1 is a diagram showing a known form of connection for phase-compensation; Fig. 2 is a diagram of a winding according to the present invention; and Fig. 3 is an explanatory diagram.

In the case of the well known phase-compensation on the individual loading coils, the two condensers are connected cross-wise between the two windings of a loading coil, as at A B and A B in Fig. 1', and the capacity C of each individual condenser is made from 0.4 to 0.8, of the capacity of a complete coilsection. According to the present invention,- the two windings A B and A B are laid bifilarly in themanner shown in Fig. 2 so that the terminals A and B of the outgoing conductor and return conductor respectively, lie on each other, and so also the opposite terminals B and A The system of cap-acities so produced between the two windings is diagrammatically shown in Fig. 3, in which as in Fig.1, A B and A B represent the coils in two longitudinal conductors of a physical circuit. Every two points which lie directly on each other in Fig. 2 are represented in Fig. 3 by two points which lie symmetrically with respect to the centre of symmetry 0. A B and B A are suchpairs, as already indicated. Other pairs are represented by E F D D F E If the two elements of length (181 and (Z82 are regarded in close proximity of E or F then the differential capacity'dC lies between the two. The same differential capacity lies between equally large elements of length in the neighborhood. of other symmetrical pairs of points.

The bifilar winding can, for example, be constructed according to the German patent application A. 48,553/21g, so that the wires used lie parallel to each other in their whole length, and are covered together, so

If the bifilar windingis so arranged that its capacity is 0.4 to 0.8 of thatof the complete loading section, the arrangement can serve for the complete phase-compensation. But

even if the self-capacity of the coil is not brought to this comparatively high value, the capacity of the two halves of the coil with respect to each other, which is produced by the bifilar winding, will reduce the variation of the transmission time for diiierent frequencies and exert a favorable effect with regard to disturbing resonant effects. The

self-capacity of the coil-halves with respect to each other can, if necessary, also be brought to the most favorable value by special smaller condensers arranged between them.

The bifilar winding is, in fact, the simplest method for creating the capacity relations required for phase-compensation without special condensers in a loading unit. But the fundamental idea of the invention comprises any kind of winding which attains this without special additional condensers.

.The bifilar winding itself need not be constructed just according to the simple scheme of Figs. 2 and 3. It will sometimes be advantageous to sub-divide the. coil-halves A B and A B further, so that the points A and 13 do not come into close proximity with the points B and A but with other points of the other half of the coil. It is then possible to give coils of equal self-inductance a difl'erent efi'ective self-capacity according to the capacity of the section of the line, and on the other hand, to obtain'the same effective self-capacity also for coils of different inductance.

The method can in the same sense also be extended to the moreor less complete compensation in the case of phantomed lines.

What is claimed is:

1. A loading coil for, transmission lines having a self-capacity substantially suflicient to compensate for the tendency of the line to produce a greater transmission delay for certain of the message frequencies than for others. v

2. A loading'coil for transmission lines having a self-capacity designed to constitute a from four-tenths to eight-tenths of the capacity of an entire section of the transmission me. I

3. A loading coil for, transmissionlines having a winding for connection in each side of the line, the wires for the two windings being laid together and wound bifilarly.

4.A loading coil for transmission lines having a winding for connection in each side of the line, the wires for the two windings being laid together and wound bifilarly, and the adjacent leads at either end of the coil being connected to line wires extending in opposite directions and in different sides 01 t e circuit.

In witness whereof, we have hereunto sei our hands this'3rd day of May, 1930.

HANS BUSCH. ALFRED BYK. 

